Compound semiconductor device epitaxial growth substrate, semiconductor device, and manufacturing method thereof

ABSTRACT

A compound semiconductor device epitaxial growth substrate, wherein a semiconductor substrate, a substrate protective layer made of a material that is different from the material of the substrate, a middle layer for making separation of the semiconductor substrate and a compound semiconductor device layer possible, and a compound semiconductor device layer that is formed through epitaxial growth are layered in this order; and a semiconductor device which uses the compound semiconductor device layer that is gained by separating the semiconductor substrate, the substrate protective layer and the middle layer from this compound semiconductor device epitaxial growth substrate; as well as manufacturing methods for these.

This nonprovisional application is based on Japanese Patent ApplicationNo. 2004-262854 filed with the Japan Patent Office on Sep. 9, 2004, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to reduction in cost of a compoundsemiconductor device epitaxial growth substrate which is manufacturedthrough epitaxial growth, and in particular, to reduction in cost of asemiconductor device such as a high efficiency multijunction-typecompound solar cell. In addition, the present invention relates toreduction in cost of a semiconductor substrate that is used forepitaxial growth by reusing the substrate.

2. Description of the Background Art

In the case of a semiconductor device that needs a large amount ofepitaxial films having a large area, such as a solar cell, it isrequired that the material cost is as low as possible. Concerning thematerial cost, the ratio of the cost of the substrate is large, andtherefore, ideas for reducing the material cost by means of techniquessuch as reusing the substrate after peeling the substrate from theelement have been put forth for a long time.

As for a technology where a semiconductor substrate for epitaxial growthis reused after the substrate is separated from a compound semiconductordevice that has been epitaxially grown, a conventional method is known,where pores are formed in, for example, the surface of a substrate, andafter that, an element layer is epitaxially grown, and a great number ofvoids which exist in the portion where the pores have been formed(middle layer) are cut through so as to mechanically separate thesubstrate from the element layer. According to this method, however, thepores remain on the surface of the substrate, and therefore, flatteningor cleaning through surface processing becomes necessary.

In addition, a conventional method is also known, where an atomdisplaced layer is formed in a portion that is extremely shallow fromthe surface of the substrate, by means of ion implantation, and afterthat, an element layer is epitaxially grown and the atom displaced layer(middle layer) is cut through so as to mechanically separate thesubstrate from the element layer, and thereby, the substrate is reused.According to this method, however, the surface of the substrate isdamaged, and therefore, flattening or cleaning through surfaceprocessing becomes necessary.

Furthermore, a method where an element layer is epitaxially grown aftera middle layer that can be selectively etched has been formed on thesurface of the substrate and the middle layer is etched and removed, andthereby, the substrate and the element layer are separated from eachother through chemical treatment is also known as a conventionaltechnology for reusing a substrate. According to this method, however, alayer that has deteriorated due to a chemical change remains on thesurface of the substrate, and therefore, flattening or cleaning throughsurface processing, again, becomes necessary.

As described above, any method which is known as a conventionaltechnology for reusing a substrate has a problem where the surface ofthe substrate becomes coarse or polluted after the separation, andrequires processing for flattening or cleaning, such as polishing on thesurface of the substrate, lapping or the like. Therefore, cost becomeshigh, due to surface processing, and in addition, a problem arises,where the number of times that use is possible is reduced due toreduction in the thickness of the substrate, and the yield is reduceddue to cracking of the substrate.

Here, Electron Lett. 35, p. 1024, by B. Asper et al. (1999), Appl. Phys.Lett. 76, p. 2131, by J Schermer et al. (2000) and 19^(th) EuropeanPhotovoltanic Solar Energy Conference, 7-11, Jun. 2004, Paris, France,pp. 169-172 by M. M. A. J. Voncken et al. (2004), for example, can becited as documents that disclose conventional technologies concerningthe present technology.

The present invention is provided in order to solve the aforementionedproblems, and an object thereof is to provide a compound semiconductordevice epitaxial semiconductor growth substrate where an element layercan be formed through epitaxial growth again after the substrate and theelement layer that has been epitaxially grown have been separated fromeach other without causing an increase in the cost due to surfaceprocessing of the substrate, such as polishing or lapping, a reductionin the number of times that use is possible due to reduction in thethickness of the substrate, or a problem of reduction in the yield dueto cracking of the substrate, as well as a semiconductor device thatuses such a substrate, and a manufacturing method of the same.

SUMMARY OF THE INVENTION

The present invention provides a compound semiconductor device epitaxialgrowth substrate characterized in that a semiconductor substrate, asubstrate protective layer made of a material that is different from thematerial of the substrate, a middle layer for making-separation of thesemiconductor substrate and a compound semiconductor device layerpossible, and a compound semiconductor device layer that is formedthrough epitaxial growth are layered in this order.

In accordance with this compound semiconductor device epitaxial growthsubstrate of the present invention, the element layer and thesemiconductor substrate can be separated at the middle layer, andthereby, a semiconductor substrate where a flat and clean surface ismaintained can be gained, by removing the substrate protective layer onthe semiconductor substrate after the separation.

According to the present invention, it is preferable for theaforementioned substrate protective layer to be removable throughetching with an etching selection ratio of no less than 80% against thesemiconductor substrate.

In addition, it is preferable for the aforementioned substrateprotective layer according to the present invention to lattice matchwith the semiconductor substrate.

In addition, it is preferable for the aforementioned middle layeraccording to the present invention to be made of a material that can beetched with a liquid or a gas which does not etch the substrate or theelement layer.

It is preferable for the aforementioned semiconductor substrate to beGaAs and for the substrate protective layer to be In_(0.5)Ga_(0.5)P,(AlGa)_(0.5)In_(0.5)P or Al_(x)Ga_(1-x)As (x>0.3) in the compoundsemiconductor device epitaxial growth substrate of the presentinvention.

The present invention also provides a semiconductor device which uses acompound semiconductor device layer that is gained by separating thesemiconductor substrate, the substrate protective layer and the middlelayer from the aforementioned compound semiconductor device epitaxialgrowth substrate.

The present invention also provides a manufacturing method of a compoundsemiconductor device epitaxial growth substrate that includes the stepsof: removing a middle layer from a compound semiconductor deviceepitaxial growth substrate where a semiconductor substrate, a substrateprotective layer made of a material that is different from the materialof the substrate, a middle layer for making the separation of thesemiconductor substrate and a compound semiconductor device layerpossible, and a compound semiconductor device layer that is formedthrough epitaxial etching are layered in this order so as to separatethe semiconductor substrate and the compound semiconductor device layer;removing the substrate protective layer through etching so as to exposethe surface of the semiconductor substrate; and sequentially growing asubstrate protective layer, a middle layer and a compound semiconductordevice layer on the exposed semiconductor substrate.

In addition, the present invention provides a manufacturing method of asemiconductor device, characterized in that a semiconductor device ismanufactured using a compound semiconductor device layer that is gainedin accordance with the aforementioned manufacturing method of a compoundsemiconductor device epitaxial growth substrate.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a compound semiconductordevice epitaxial growth substrate 1 according to one preferable exampleof the present invention;

FIG. 2 is a diagram illustrating a manufacturing method of a compoundsemiconductor device epitaxial growth substrate according to the presentinvention; and

FIG. 3 is a diagram schematically showing a solar cell that is gained inaccordance with a manufacturing method according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram schematically showing a compound semiconductordevice epitaxial growth substrate 1 according to one preferable exampleof the present invention. Compound semiconductor device epitaxial growthsubstrate 1 of the present invention has a basic structure where asubstrate protective layer 3, a middle layer 4 and a compoundsemiconductor device layer (element layer) 5 are sequentially layered ona semiconductor substrate 2. Here, “upward direction” of the substrateindicates the direction upward, as opposed to downward, along thethickness of the substrate. Here, “semiconductor device” in the presentspecification includes a compound semiconductor device, and concretely,a solar cell (a multijunction solar cell where a single or a number ofsolar batteries from among a GaAs solar cell, an InGaAs solar cell, anInGaP solar cell, an AlInGaP solar cell and an InGaNAs solar cell areconnected to each other through tunnel junctions) and the like can becited.

As for semiconductor substrate 2 according to the present invention,conventional materials that have been widely used in the present fieldcan be used without particular limitation as the material for formingthe semiconductor substrate. GaAs, Ge, InP, sapphire, Si and the likecan be cited as examples of the material for forming this semiconductorsubstrate 2. In particular, GaAs is preferable, because this allows highquality layers with a low crystal defect density to lattice match andgrow for the formation of a high efficiency solar cell element.

Though the thickness of semiconductor substrate 2 is not particularlylimited, it is preferable for it to be 100 μm to 10000 μm, and it ismore preferable for it to be 300 μm to 1000 μm. In the case where thethickness of semiconductor substrate 2 is less than 100 μm, thesubstrate tends to easily warp during growth and easily break duringhandling, whereas in the case where the thickness exceeds 10 000 μm,support of the substrate within the device for growth tends to becomecomplicated or heavy, making it difficult to handle.

Substrate protective layer 3 is formed of a material that is differentfrom that of the aforementioned semiconductor substrate 2, and it ispreferable for the material to be removable through etching with anetching selection ratio of no less than 80% (more preferably, no lessthan 98%) against semiconductor substrate 2. Such an etching selectionratio makes it possible for only substrate protective layer 3 onsemiconductor substrate 2 to be efficiently removed through etchingafter the separation of substrate protective layer 3 and compoundsemiconductor device epitaxial element layer 5 in accordance with thebelow described manufacturing method of a compound semiconductor deviceepitaxial growth substrate of the present invention, and thereby,semiconductor substrate 2 where a flat and clean surface is maintainedcan easily be collected, so that it can be reused for the manufacture ofa compound semiconductor device epitaxial growth substrate.

In addition, it is preferable for substrate protective layer 3 accordingto the present invention to lattice match semiconductor substrate 2.This is because, in the case where substrate protective layer 3 latticematches semiconductor substrate 2, no atomic layers from the surface ofthe substrate to the vicinity of the protective layer warp, and thus,little damage is caused to the surface of the substrate, and therefore,the number of times of reuse of the substrate can be increased.

The material that forms substrate protective layer 3 according to thepresent invention is not particularly limited, as long as it isdifferent from that of the aforementioned semiconductor substrate 2, andInGaP, AlGaInP, AlGaAs, GaAsP and the like can be cited as examples whena GaAs substrate is used. In particular, In_(0.5)Ga_(0.5)P,(AlGa)_(0.5)In_(0.5)P or Al_(x)Ga_(1-x)As (x>0.3) are preferable,because they lattice match the substrate and have an etching selectionratio of no less than 80%.

It is preferable for the thickness of substrate protective layer 3 to be0.01 μm to 2 μm, and it is more preferable for it to be 0.05 μm to 0.5μm. This is because in the case where the thickness of substrateprotective layer is less than 0.01 μm, the layer is too thin and tendsto partially peel during etching, whereas in the case where thethickness exceeds 2 μm, the cost of epitaxial growth tends to increase.

Middle layer 4 is formed between substrate protective layer 3 andelement layer 5 in order to make the separation of semiconductorsubstrate 2 and element layer 5 possible, in accordance with the belowdescribed manufacturing method of a compound semiconductor deviceepitaxial growth substrate of the present invention, and it ispreferable to form the middle layer of a material which can be etchedwith a liquid or a gas that does not etch the substrate, the protectivelayer or the element layer. AlAs, Al_(x)Ga_(1-x)As (x>0.5), InGaP,AlInGaP and the like can be cited as examples of this material, in thecase where the substrate is formed of an appropriate material selectedfrom the above, and the element layer is formed of an appropriatematerial that is selected from below. In particular, AlAs,Al_(x)Ga_(1-x)As (x>0.5), In_(0.5)Ga_(0.5)P and (AlGa)_(0.5)In_(0.5)Pare preferable. As for the liquid or gas for etching, a hydrofluric acidbased solution, a hydrochloric acid based solution, a sulfuric acidbased solution, an ammonium based solution, a potassium hydroxide basedsolution, a chlorine based gas, a fluorine based gas and the like can becited as examples.

It is preferable for the thickness of middle layer 4 to be 0.003 μm to 2μm, and it is more preferable for it to be 0.005 μm to 0.1 μm. This isbecause in the case where the thickness of middle layer 4 is less than0.003 μm, a region where the middle layer is not formed tends to formwithin the surface of the substrate, whereas in the case where thethickness exceeds 2 μm, the amount of etching increases and the etchingrate tends to lower.

The material of element layer 5 is not particularly limited, as long asit is made up of one or more layers which are formed on theaforementioned middle layer 4 through epitaxial growth and can be formedof a conventionally known appropriate material in accordance with theapplication. It is preferable for element layer 5 to have a two-layerstructure where the two layers are connected via a tunnel junction inthe structures of the rear surface electrical field layer, the baselayer, the emitter layer and the window layer, in order to gain a highlyefficient solar cell. In element layer 5 of the example shown in FIG. 1,a p-InGaP layer, which is a rear surface electrical field layer 11, ap-GaAs layer, which is a base layer 12, an n-GaAs layer, which is anemitter layer 13, and an AlInP layer, which is a window layer 14, areformed as the first layer structure. In addition, a p-AlInP layer, whichis a rear surface electrical field layer 16, a p-InGaP layer, which is abase layer 17, an n-InGaP layer, which is an emitter layer 18, and anAlInP layer, which is a window layer 19, are formed as the second layerstructure on top of the first layer structure with an InGaP layer and anAlGaAs layer, which make up a tunnel junction layer 15, in between.Furthermore, an n-GaAs layer, which is a contact layer 20, is formed asthe topmost surface layer. An appropriate thickness of each layer can beselected within a preferable range, in accordance with the functionthereof. The layered structure of element layer 5 shown in FIG. 5 is, ofcourse, illustrative, and element layer 5 according to the presentinvention is not limited to this.

Compound semiconductor device epitaxial growth substrate 1 of thepresent invention is provided with substrate protective layer 3 made ofa material that is different from the material of the substrate, andformed on semiconductor substrate 2 and middle layer 4 for making theseparation of substrate 2 and element layer 5 possible, which aresequentially layered between semiconductor substrate 2 and compoundsemiconductor device layer 5, as described above. This compoundsemiconductor device epitaxial growth substrate 1 of the presentinvention allows element layer 5 and semiconductor substrate 2 to beseparated at middle layer 4, and thereby, semiconductor substrate wherea flat and clean surface is maintained can be gained, by removingsubstrate protective layer 3 on semiconductor substrate 2 after theseparation.

Compound semiconductor device epitaxial growth substrate 1 of thepresent invention that is provided with the aforementioned structure canbe manufactured in accordance with, for example, the followingprocedure.

First, a vertical type MOCVD device is used to sequentially grow andlayer substrate protective layer 3 and middle layer 4 on semiconductorsubstrate 2. In the case where, for example, a GaAs substrate is used assemiconductor substrate 2, an InGaP layer is formed as substrateprotective layer 3, and an AlAs layer is formed as middle layer 4, TMI(trimethyl indium), TMG and PH₃ (phosphine) can be used as the materialsfor the growth of the InGaP layer, and in addition, TMA (trimethylaluminum) and AsH₃ (arsine) can be used as the materials for the growthof the AlAs layer.

Furthermore, element layer 5 is epitaxially grown on top of this. In thecase where element layer 5 which has a layered structure as in theexample shown in FIG. 1 is formed, a p-InGaP layer, which is rearsurface electrical field layer 11, a p-GaAs layer, which is base layer12, an n-GaAs layer, which is emitter layer 13, and a AlInP layer, whichis window layer 14, are formed as the first layer structure. Inaddition, a p-AlInP layer, which is rear surface electrical field layer16, a p-InGaP layer, which is base layer 17, an n-InGaP layer, which isemitter layer 18, an AlInP layer, which is window layer 19, and ann-GaAs layer, which is contact layer 20, are sequentially formed andlayered on top of the first layer structure as the second layerstructure, with an InGaP layer and an AlGaAs layer, which make up tunneljunction layer 15, in between. TMI (trimethyl indium), TMG (trimethylgallium) and PH₃ (phosphine) can be used as the materials for the growthof the InGaP layers, and TMG and AsH₃ (arsine) can be used as thematerials for the growth of the GaAs layers, in the same manner as inthe above. In addition, TMA (trimethyl aluminum), TMI and PH₃ can beused as the materials for the growth of the AlInP layers. SiH₄(mono-silane) can be used as an impurity for the formation of n-typelayers, and DEZn can be used as an impurity for the formation of p-typelayers during the growth of all of the GaAs layers, InGaP layers andAlInP layers. In addition, TMI, TMG and AsH₃ can be used as thematerials, and CBr₄ (carbon tetrabromide) can be used as a p-typeimpurity for the growth of the AlGaAs layer that forms the tunneljunction. In this manner, the compound semiconductor device epitaxialgrowth substrate 1 having a structure as in the example shown in FIG. 1can be manufactured.

It is preferable for the temperature for growing layers other than thetunnel junction layer to be within a range from 600° C. to 700° C., inorder to increase the lifetime of minor carriers, while it is preferablefor the temperature for growing the tunnel junction layer to be within arange from 500° C. to 600° C., in order to prevent re-vaporization ofthe impurity, so that the impurity can be doped at a high concentration.

FIG. 2 is a diagram illustrating a manufacturing method of a compoundsemiconductor device epitaxial growth substrate according to the presentinvention, and FIG. 3 is a diagram schematically showing a solar cell asone example of a semiconductor device that is gained in accordance withthe manufacturing method of the present invention. The present inventionalso provides a manufacturing method of a compound semiconductor deviceepitaxial growth substrate that includes the steps of: removing middlelayer 4 from compound semiconductor device epitaxial growth substrate 1which is provided with semiconductor substrate 2, substrate protectivelayer 3 made of a material that is different from the material of thesubstrate and formed on semiconductor substrate 2, and compoundsemiconductor device layer 5 that is formed on substrate protectivelayer 3 through epitaxial growth, and which further has middle layer 4for making the separation of substrate 2 and element layer 5 possiblebetween substrate protective layer 3 and compound semiconductor devicelayer 5, so that the semiconductor substrate and the compoundsemiconductor device layer are separated; removing the substrateprotective layer through etching so that the surface of semiconductorsubstrate 2 is exposed; and sequentially growing substrate protectivelayer 3, middle layer 4 and compound semiconductor device layer 5 on theexposed semiconductor substrate 2.

Prior to implementing the manufacturing method of a compoundsemiconductor device epitaxial growth substrate of the presentinvention, a process is carried out on element layer 5 of compoundsemiconductor device epitaxial growth substrate 1 having, for example, astructure as shown in FIG. 1, that has been prepared as described aboveso that a cell precursor (precursor of a solar cell) is formed. First, aGaAs layer 21 is formed on contact layer 20 of compound semiconductordevice epitaxial growth substrate 1 shown in FIG. 1, and after that, asurface electrode 25 having a desired pattern is formed. In theformation of surface electrode 25, first, a resist where windows arecreated in a desired electrode pattern form in accordance with aphotolithographic method, for example, is applied, and the substrate isplaced in a vacuum vapor deposition device so as to form a resist, andafter that, a layer (for example, 100 nm) made of Au that includes 12%of Ge, for example, is formed in accordance with a resistance heatingmethod, and then, an Ni layer (for example, 20 nm) and an Au layer (forexample, 5000 nm) are sequentially formed in accordance with an EB vapordeposition method, and thus, the electrode is formed with a desiredpattern in accordance with, for example, a lift-off method.

Next, surface electrode 25 is used as a mask, and the portion of GaAslayer 21 where surface electrode 25 is not formed is etched using, forexample, an alkaline solution. Subsequently, a resist with windowsopened in a mesa-etching pattern is formed in accordance with aphotolithographic method, and the epitaxial layer in the portions wherewindows are open is etched with an alkaline solution and an acidsolution, so that middle layer 4 is exposed (element layer 5 thatremains after etching and where surface electrode 25 is formed isreferred to as “cell precursor 31”).

Next, support substrates 33 made of plastic are made to adhere to cellprecursors 31 after wax 32 has been applied to the surface of cellprecursors 31, so as to form the structure shown in FIG. 2. Apiezon wax,for example, is appropriate for use as wax 32. In addition, platesformed of glass, ceramics or Si having high chemical proof properties,for example, can be used as support substrates 33. Support substrates 33can be made adherent using, for example, a removable wax or resist.

The structure of FIG. 2 is formed in this manner, and after that, theaforementioned manufacturing method of a compound semiconductor deviceepitaxial growth substrate is implemented according to the presentinvention. Namely, in the initial step, middle layer 4 is first removedso that semiconductor substrate 2 and compound semiconductor devicelayer 5 (cell precursor 31 in the example shown in FIG. 2) areseparated. The structure shown in FIG. 2 is immersed in a hydrofluoridesolution, and thereby, removal of middle layer 4 can be carried out, byetching middle layer 4. Each cell precursor 31 after the separation canbe formed into a structure (solar cell) as shown in FIG. 3, by formingelectrode (rear surface electrode) 26 in accordance with a method suchas vapor deposition, sputtering, electrolytic plating, non-electrolyticplating, ion plating, spraying, adhesion or printing, and after that,melting wax at a high temperature so as to separate the precursor fromthe support substrate, and then, immersing the precursor in an organicsolvent so as to remove wax 32.

In the next step, substrate protecting layer 3 is removed fromsemiconductor substrate 2 through etching, so that the surface ofsemiconductor substrate 2 is exposed. Semiconductor substrate 2 that isgained in this manner has a flat and clean substrate surface, unlikeconventional substrates. As described above, substrate protective layer3 is preferably selected so as to be removable through etching at anetching selection ratio of no less than 80% against the semiconductorsubstrate, and thereby, a flat and clean substrate surface can be easilygained without causing damage to the surface of the substrate. Etchingof substrate protective layer 3 can be carried out with an appropriateetching solution under appropriate conditions, in accordance with thematerial that forms the substrate protective layer. In the case where,for example, an InGaP layer is used as substrate protective layer 3, asshown in FIG. 1, substrate protective layer 3 can be removed throughetching, by immersing the substrate in an HCl solution.

After that, substrate protective layer 3, middle layer 4 and compoundsemiconductor device layer 5 are sequentially grown on the exposedsemiconductor substrate 2. At this time, it is preferable to provideseveral nm or more of the same material as the substrate as a bufferlayer between the substrate and the substrate protective layer in aconventional process through epitaxial growth. Before carrying out thisstep, it is preferable to rinse semiconductor substrate 2 with ultrapure water, and after that, dry it by means of N₂ blowing. In addition,in a conventional process, before the epitaxial growth, it is preferableto etch the substrate by approximately several nm from the surface ofthe substrate with the solution with which the substrate is etched. Theformation of substrate protective layer 3, middle layer 4 and compoundsemiconductor device layer 5 may be carried out in the same manner asdescribed above. Compound semiconductor device epitaxial growthsubstrate 1 having a structure as shown in FIG. 1 is manufactured againusing semiconductor substrate 2 that has been collected as describedabove. According to the manufacturing method of a compound semiconductordevice epitaxial growth substrate of the present invention, this cycleis repeated, so that semiconductor substrate 2 is reused many times, andthereby, solar cells as shown in FIG. 3 can be manufactured.

Here, as described above, the present invention also provides asemiconductor device (for example, a solar cell as that shown in FIG. 3)which uses a compound semiconductor device layer that is gained byseparating the semiconductor substrate, the substrate protective layerand the middle layer from the compound semiconductor device epitaxialgrowth substrate of the present invention.

In addition, the scope of the present invention also includes amanufacturing method of a semiconductor device, characterized in that asemiconductor device is manufactured using a compound semiconductordevice using that is gained in accordance with the aforementionedmanufacturing method of a compound semiconductor device epitaxial growthsubstrate of the present invention.

EXAMPLES

In the following, the present invention is more concretely described,but the present invention is not limited to these examples.

Example 1

First, the layer structure shown in FIG. 1 was fabricated on an n-typeGaAs substrate, which is semiconductor substrate 2, by means of an MOCVDmethod. That is to say, a GaAs substrate (1E18 cm⁻³, Si doped) having adiameter of 50 mm was placed in a vertical type MOCVD device, and first,0.1 μm of a In_(0.5)Ga_(0.5)P layer was formed as substrate protectivelayer 3. Subsequently, 0.02 μm of an AlAs layer was formed as middlelayer 4 for the separation through etching, 0.1 μm of an InGaP layer wasgrown, for stopping etching, and layers were sequentially grown for asolar cell layer structure, and thus, element layer 5 was formed.

The temperature for growth was 700° C., and TMG (trimethyl gallium) andAsH₃ (arsine) were used as the materials for the growth of the GaAslayers. TMI (trimethyl indium), TMG and PH₃ (phosphine) were used as thematerials for the growth of the InGaP layers. SiH₄ (mono-silane) wasused as an impurity for the formation of an n-type layer, and DEZn wasused as an impurity for the formation of a p-type layer during thegrowth of all of GaAs, InGaP and AlInP layers. TMI, TMG and AsH₃ wereused as the materials for the growth of the AlGaAs layer that forms thetunnel junction, where CBr₄ (carbon tetrabromide) was used as a p-typeimpurity.

A resist where windows were open for an electrode pattern was formed onthe contact layer (n-type GaAs layer) on the surface of the epitaxiallayer in accordance with a photolithographic method, the substrate wasplaced in a vacuum vapor deposition device, so that a layer (100 nm)made of Au that contains 12% of Ge was formed on the formed resist inaccordance with a resistance heating method, and after that, an Ni layer(20 nm) and an Au layer (5000 nm) were sequentially formed in accordancewith an EB vapor deposition method. After that, a surface electrode in adesired pattern was formed in accordance with a lift-off method. Next,the surface electrode was used as a mask, and the portion of the GaAscontact layer where the electrode was not formed was etched with analkaline solution.

Subsequently, a resist with windows opened in a mesa etching pattern wasformed in accordance with a photolithographic method, and the portionsof the epitaxial layer where the windows were open were etched with analkaline solution and an acid solution, so that the AlAs layer, which ismiddle layer 4, was exposed.

Next, wax was applied and a plastic plate was made to adhere to thelight receiving surface of the cell, excluding the mesa etching portion,so that a cross sectional structure as that shown in FIG. 2 wasfabricated. After that, the wafer was immersed in an Hf solution, andthe AlAs middle layer beneath the cell layer was etched and removed fromthe mesa etching portion, and thereby, the cell layer and the substratewere separated. After that, an electrode was formed on the rear surfaceof each cell, and then, the wax was removed, so that a solar cell wascompleted in the first process, so as to have a structure as that shownin FIG. 3. The size of the cell was 10 mm×10 mm, and 12 cells werefabricated from a substrate having a diameter of 50 mm.

After that, the InGaP layer, which is substrate protective layer 3,formed on the substrate side, was removed through etching with HCl, sothat the surface of the GaAs substrate was exposed. The substrate wasrinsed with ultra pure water, and after that, dried through N₂ blowing,placed into the MOCVD device again, and the structure of FIG. 1 wasagain epitaxially grown. The above described process was carried outagain, and a solar cell was completed in the second process, so as tohave the same structure as that shown in FIG. 2.

Evaluation of cell characteristics was carried out with a solarsimulator which radiates AM 1.5G standard solar beams, so as to measurethe current voltage characteristics at the time of radiation of thebeams, and the short circuit current, the open voltage and theconversion efficiency were measured. Table 1 shows a comparison ofvarious characteristics between the cells that were fabricated in thefirst and second processes. TABLE 1 Voc(V) Isc(mA) F.F. Eff(%) FIRSTPROCESS 2.41 13.7 0.85 28.2 SECOND PROCESS 2.42 13.6 0.85 28.2

Characteristics which were essentially the same as those of the cells ofthe first process were gained in the cells of the second process, whichwere fabricated on the reused substrate, and thus, it was confirmed thatsubstrates can be reused effectively according to the present invention.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A compound semiconductor device epitaxial growth substrate, wherein asemiconductor substrate, a substrate protective layer made of a materialthat is different from the material of the substrate, a middle layer formaking separation of the semiconductor substrate and a compoundsemiconductor device layer possible, and a compound semiconductor devicelayer that is formed through epitaxial growth are layered in this order.2. The compound semiconductor device epitaxial growth substrateaccording to claim 1, wherein said substrate protective layer can beremoved through etching at an etching selection ratio of no less than80% against the semiconductor substrate.
 3. The compound semiconductordevice epitaxial growth substrate according to claim 1, wherein saidsubstrate protective layer lattice matches the semiconductor substrate .4. The compound semiconductor device epitaxial growth substrateaccording to claim 1, wherein said middle layer is made of a materialwhich can be etched with a liquid or a gas that does not etch thesubstrate or the element layer.
 5. The compound semiconductor deviceepitaxial growth substrate according to claim 1, wherein saidsemiconductor substrate is GaAs, and the substrate protective layer isIn_(0.5)Ga_(0.5)P, (AlGa)_(0.5)In_(0.5)P or Al_(x)Ga_(1-x)As (x>0.3). 6.A semiconductor device which uses the compound semiconductor devicelayer that is gained by separating the semiconductor substrate, thesubstrate protective layer and the middle layer from the compoundsemiconductor device epitaxial growth substrate according to claim
 1. 7.A manufacturing method of a compound semiconductor device epitaxialgrowth substrate, comprising the steps of: removing a middle layer formaking possible separation of a semiconductor substrate and a compoundsemiconductor device layer that is formed through epitaxial growth froma compound semiconductor device epitaxial growth substrate, wherein thesemiconductor substrate, a substrate protective layer made of a materialthat is different from the material of the substrate, the middle layer,and the compound semiconductor device layer are layered in this order,so that the semiconductor substrate and the compound semiconductordevice layer are separated; removing the substrate protective layerthrough etching so as to expose the surface of the semiconductorsubstrate; and sequentially growing a substrate protective layer, amiddle layer and a compound semiconductor device layer on the exposedsemiconductor substrate.
 8. A manufacturing method of a semiconductordevice, wherein a semiconductor device is manufactured using thecompound semiconductor device layer that is gained in accordance withthe manufacturing method of a compound semiconductor device epitaxialgrowth substrate according to claim 7.